1. Field of the Invention
The present invention relates to a mobile communication system. More particularly, the present invention relates to a method and apparatus for transmitting/receiving channels between a base station and a mobile terminal efficiently in a mobile communication supporting massive Multiple Input Multiple Output (MIMO) transmission.
2. Description of the Related Art
The mobile communication system has evolved into a high-speed, high-quality wireless packet data communication system to provide data and multimedia services beyond the early voice-oriented services. Recently, various mobile communication standards, such as High Speed Downlink Packet Access (HSDPA), High Speed Uplink Packet Access (HSUPA), Long Term Evolution (LTE), and LTE-Advanced (LTE-A) defined in 3rd Generation Partnership Project (3GPP), High Rate Packet Data (HRPD) defined in 3rd Generation Partnership Project-2 (3GPP2), and 802.16 defined in Institute of Electrical and Electronics Engineers (IEEE), have been developed to support the high-speed, high-quality wireless packet data communication services. Particularly, LTE corresponds to a communication standard developed to support high speed packet data transmission and to maximize the throughput of the radio communication system with various radio access technologies. LTE-A corresponds to an evolved version of LTE to improve the data transmission capability.
LTE is characterized by 3GPP Release 8 or 9 capable base station and terminal (User Equipment (UE)) while LTE-A is characterized by 3GPP Release 10 capable base station and UE. As a key standardization organization, 3GPP continues standardization of the next release for more improved performance beyond LTE-A.
The existing 3rd and 4th generation wireless packet data communication systems (such as HSDPA, HSUPA, HRPD, and LTE/LTE-A) adopt Adaptive Modulation and Coding (AMC) and Channel-Sensitive Scheduling techniques to improve the transmission efficiency. AMC allows the transmitter to adjust the data amount to be transmitted according to the channel condition. For example, the transmitter is capable of decreasing the data transmission amount for bad channel condition so as to fix the received signal error probability at a certain level or increasing the data transmission amount for good channel condition so as to transmit large amount of information efficiently while maintaining the received signal error probability at an intended level. Meanwhile, the channel sensitive scheduling allows the transmitter to serve the user having good channel condition selectively among a plurality of users so as to increase the system capacity as compared to allocating a channel fixedly to serve a single user. This increase in system capacity is referred to as multi-user diversity gain. In brief, the AMC method and the channel-sensitive scheduling method are methods for receiving partial channel state information being fed back from a receiver, and applying an appropriate modulation and coding technique at the most efficient time determined depending on the received partial channel state information.
In a case of using AMC along with MIMO transmission scheme, it may be necessary to consider a number of spatial layers and ranks for transmitting signals. In this case, the transmitter determines the optimal data rate in consideration of the number of layers for use in MIMO transmission.
Recent research aims to replace Code Division Multiple Access (CDMA) used in the legacy 2nd and 3rd mobile communication systems with Orthogonal Frequency Division Multiple Access (OFDMA) for the next generation mobile communication system. The 3GPP and 3GPP2 are in the middle of the standardization of OFDMA-based evolved system. OFDMA is expected to provide superior system throughput as compared to the CDMA. One of the main factors that allow OFDMA to increase system throughput is the frequency domain scheduling capability. As channel sensitive scheduling increases the system capacity using the time-varying channel characteristic, OFDM can be used to obtain more capacity gain using the frequency-varying channel characteristic.
As described above, LTE supports MIMO using a plurality of transmit and receive antennas. MIMO corresponds to a technique for transmitting information multiplexed spatially in adaptation to instantaneous channels established with plural transmit and receive antennas. The MIMO transmission is capable of multiplexing plural data streams spatially onto a single time-frequency resource so as to be able to increase the data rate a few folds as compared to the non-MIMO transmission. LTE Release 11 supports the MIMO transmission with up to 8 transmit antennas and up to 8 receive antennas. In this case, up to 8 data streams can be multiplexed spatially, resulting in increase of data rate up to 8 times more than non-MIMO transmission.
Typically, MIMO is classified into one of Single-User MIMO (SU-MIMO) for transmitting spatially multiplexed multiple data streams to a single user and Multi-User MIMO (MU-MIMO) for transmitting spatially multiplexed multiple data streams to multiple users.
In contrast to the SU-MIMO transmitting the spatially multiplexed multiple data streams to a single UE, the MU-MIMO is capable of transmitting the spatially multiplexed multiple data streams to multiple UEs. In the MU-MIMO, the evolved Node B (eNB) transmits plural data streams such that each UE is capable of receiving one or more of the data streams transmitted by the eNB. Accordingly, the MU-MIMO is advantageous especially when the number of eNB's transmit antennas is greater than the number of UE's receive antennas.
In the case of SU-MIMO, the maximum number of data streams capable of being multiplexed spatially is restricted by min(NTx, NRx) where NTx denotes the number of eNB's transmit antennas and NRx denotes the number of UE's receive antennas. Meanwhile, in the case of MU-MIMO, the maximum number of data streams capable of being multiplexed spatially is restricted by min(NTx, NMS X NRx) where NMS denotes the number of UEs.
Massive MIMO or Full Dimension MIMO is an emerging technology feasible with a few dozen to a few hundred of eNB's transmit antennas. Thus, in order to enhance the system throughput, it is required to increase the number of data streams significantly as compared to the legacy LTE system. In order to accomplish this, the massive MIMO transmission scales up the MU-MIMO for simultaneous transmission to multiple UEs by an order of magnitude.
Therefore, a need exists for a channel transmission/reception method and apparatus capable of allocating Demodulation Reference Signal (DMRS) resource guaranteeing orthogonality among a plurality of UEs in the massive MIMO system
The above information is presented as background information only to assist with an understanding of the present disclosure. No determination has been made, and no assertion is made, as to whether any of the above might be applicable as prior art with regard to the present invention.